1. Field of the Invention
The present invention relates to a telephone control system.
2. Description of the Related Art
At the present time at which information communication networks have progressed, people communicate with one another more often by telephone conversation than by correspondence. Accordingly, a situation frequently arises where an incoming call is received on a busy line connected to a telephone set. In that case, a busy signal is issued to the telephone receiver of a user who called the busy line, so that ordinarily the user calls back after a certain time period. An interrupt connection service has been devised as one technique for eliminating such an inconvenience. Regarding the actual operation of the interrupt connection service, however, several problems are involved.
By way of example, when a busy telephone line receives an incoming call from a calling party, the interrupt connection service sends an incoming call tone to the busy telephone line, thereby to notify the occurrence of the interrupt incoming call to the user of the service. However, when the interrupt connection service is employed in a single line, there is the problem that the user must disconnect the busy line once and thereafter call the opposite party having made the interrupt connection.
A technique for addressing this problem is disclosed in, for example, Japanese Unexamined Patent Publication JP-A 4-172743 (1992). This document describes a busy-status interrupt connection scheme wherein a plurality of lines are utilized, and a telephone set can be connected to another line without disconnecting the busy line connected to the telephone set, thereby to permit interrupt connections to the plurality of lines.
A so-called “button telephone set” is well suited for application to such an interrupt connection service utilizing the plurality of lines, and it is so constructed that a talk can be switched by the switching selection of an opposite party and an outside-line transfer function through the hooking manipulations of a user. Since, however, the button telephone set is not constructed so as to automatically perform the switching in response to the interrupt connection, the user himself/herself must memorize and perform accurate operations for switching the line to the opposite party of the interrupt connection.
A technique for addressing this problem is disclosed in, for example, Japanese Unexamined Patent Publication JP-A 2001-292463 (2001). This document describes a button telephone apparatus wherein a user can smoothly utilize an interrupt incoming call service without burdensome operations. The button telephone apparatus operates as stated below. When an interrupt incoming call for a telephone line as held by a slave (telephone) set A has been detected, the slave set A and another slave (telephone) set B are called up. When the slave set B has responded to the call, speech between the slave set B and the side of the interrupt incoming call can be formed. Thereafter, when the speech has been ended, a hooking signal is sent to the telephone line, while the telephone line is held, and a hold alarm is outputted to the slave set A so as to notify the end of the interrupt talk.
Furthermore, in case of an interrupt connection service utilizing a master-slave telephone system which is so constructed that a plurality of slave sets can be used for a single master (telephone) set, there is the problem that, when the slave set (or master set) is talking with an outside line, a ringing tone called a “paging tone” or an interrupt talk cannot be given forth from the master set or any other slave set to the talking slave set (or master set) for reasons of such as the protection of privacy.
A technique for addressing this problem is disclosed in, for example, Japanese Unexamined Patent Publication JP-A 5-344054 (1993). Proposed here is a cordless telephone wherein a paging signal being a ringing signal can be transmitted together with a voice signal by employing a frequency outside the bandwidth of the voice signal, and wherein, when the paging signal has been transmitted from, for example, a master set during a talk with an outside line, the outside line is held, and connection is switched for the talk between the master set and a slave set so as to permit the interrupt talk.
Even the techniques proposed in order to improve the problems concerning the actual operations of the interrupt connection services, have further problems as stated below. With the busy-status interrupt connection scheme disclosed in JP-A 4-172743, and the button telephone set disclosed in JP-A 2001-292463, the connection to the other line is possible without disconnecting the busy line connected to the telephone set, that is, the interrupt connections are possible to the plurality of lines, but there is the problem that, when the telephone set which is occupying the line and holding a talk receives an incoming call from another line anew, a user who is distant from the telephone set holding the talk cannot know the new incoming call.
With the master-slave telephone system disclosed in JP-A 5-344054, there is a problem that, when paging is performed in the off-hooking (talking) status of, for example, the slave set, the ringing tone is emitted from a loudspeaker or a bell included in the slave set, so it is heard by the talking opposite party.